1. Field of the Invention
The invention relates to the field of battery production and, more particularly, to an apparatus and method suitable for the continuous hydrosetting, drying and cooling of battery plates.
2. Background of the Related Art
The known methods of manufacturing battery plates for vehicle and industrial lead acid batteries involve the assembly of the individual battery components. The first step of manufacture is to mold a lead or lead alloy wire screen or matrix, by casting molten lead onto a grid structure. Next, a paste composed of lead oxide (i.e., free lead particles and alpha and beta forms of lead monoxide), dilute sulfuric acid and water, is pressed into the open areas of the grid. The components of the paste are blended together in proportions specified by the battery manufacturer. The pasted plates are delivered to a high-temperature flash drying oven to reduce the water content of the paste to an optimum range for subsequent processing, and to dry the outer surface of the lead paste sufficiently so that the plates can be handled in subsequent processing without the plates sticking together.
After the battery plates have been removed from the flash drying oven, they are typically manually loaded onto racks or pallets and temporarily stacked for subsequent loading into a batch-type oven. The chambers of the batch-type ovens used in the production of battery plates are commonly known as hydroset chambers. Hydroset chambers provide the necessary conditions to cure the lead oxides contained within the lead paste so as to form a crystalline structure, which is porous and provides good adhesion to the lead support. Curing also converts any free lead particles in the paste to different chemistries.
The curing process within the hydroset chamber includes three distinct stages. The first stage is the steaming, or so-called hydroset stage, which establishes the correct atmosphere for the development of basic lead sulfates within the paste, and equalizes the moisture content between the stacks of plates.
The second stage is a relatively lower level humidity treatment, which promotes the oxidation of the free lead in the paste and the conversion to monobasic, tribasic and tetrabasic lead compounds.
The third stage of curing comprises drying the hydroset plates to reduce the water content of the past to an extremely low level, which closely approaches zero. Such a low moisture level is required for active material stability.
There are two known processes widely used in the steaming or hydroset stage of battery production; namely, a manual process and the above-described process utilizing batch-type ovens. In the manual method, the pasted battery plates are placed on a pallet and covered with a wet piece of material such as burlap or canvas. The pallet is then placed in an enclosed heated area for a minimum of three days, until the hydrosetting has been completed.
The manual method has several limiting disadvantages. It requires a vast amount of floor space for storing the pallets during hydrosetting. Also, an extended period of time is required for the hydroset process to be completed. Furthermore, the manufacturer does not have close control of the progress and degree of completion of hydrosetting, and thus it is difficult to determine whether the process has been completed at a given time. Consequently, a large amount of time is wasted by allowing hydrosetting to continue longer than necessary due to the difficulty of knowing whether the hydroset process has been completed.
The hydrosetting process utilizing batch-type ovens is presently the most commonly used process because it reduces the hydroset process time to approximately forty-five hours, as compared to at least seventy-two hours for the manual hydroset process.
Most of the batch-type hydroset ovens in use today have indirect fired natural gas, steam, or electrical heating systems and water injection systems to provide the desired temperature and humidity conditions within the hydroset chamber. Microprocessor control is conventionally used to enable temperature and humidity ramping during each stage of the curing process. The batch-type oven chambers typically include a stainless steel interior to resist the adverse effects of high humidity and temperature, and an opening for loading and unloading the palletized battery plates.
The known battery manufacturing systems incorporate automated equipment in the grid casting, plate pasting, plate wrapping and formation stages. The systems do not, however, include an automated and modernized hydroset stage.
The hydroset stage of battery manufacturing in the known systems is linked closely to the battery plate flash drying systems which partially dry the pasted plates to enable the plates to be handled prior to the hydroset stage. The flashdrying and hydrosetting stages, however, consume a large amount of energy and represent a significant portion of the cost of battery plate manufacturing. In addition, the known batch-type hydroset equipment occupies a large amount of floor space and, accordingly, necessitates the use of larger, more expensive manufacturing facilities.
The known systems also require the palletizing or batching of battery plates, which is labor intensive and requires equipment for the handling of extremely heavy pallets of lead pasted plates.
Furthermore, the known hydrosetting processes are unable to achieve consistent, uniform hydrosetting of each individual battery plate. Consequently, the known processes are unable to ensure that high quality standards are consistently achieved. The known methods are limited due to the wide variability in the conditions the individual battery plates within the hydrosetting chamber are subjected to. The local conditions within the chamber are affected by factors such as the pallet stacking configuration, pallet location within the chamber relative to the locations of the air supply and return outlets, the total batch size in a particular run of battery plates, and the order of loading of a particular pallet of plates; in batch processing, the first pallet placed in the chamber is removed last. Any of these factors can cause the individual plates to be subjected to different curing conditions and, consequently, to form different free lead and moisture percentages. As a result, present battery plate production is inconsistent and the battery plates are frequently of poor quality.